I think we should clearly differentiate between:
- Questions asking how to specifically get around a limitation
- Questions asking how or if something like that is hypothetically possible
The former are mostly very specific and in my opinion not okay on the site. The latter can actually be very interesting as they don't have consequences for both the OP and the persons answering.
Note that in the ISP case, the user isn't doing anything illegal yet (correct me if I'm wrong), it's just against the Terms of Service. If the ISP found out, they'd probably just cancel the account. Kindly reminding them that this may result in a cancellation should be enough. The fact that what they asked to do is not really possible also means there will be no answers that would help him get around these limitations. Not a problem for SU in my opinion.
If the user however asked how to "hack" something, this would definitely be illegal and should therefore be closed right away.
I think in the case of questions that ask how to deliberately circumvent restrictions, which would be against ToS, we just should not answer. I only know this from Hackintosh questions, which are a legal gray area too. They're closed because clearly Super User will not serve as a guide on how to hack OS X. In the end, I don't want to be the one who instigates a potentially illegal action. I'd just keep out of it.
The broader topic of DRM on the other side is something completely different, because in DRM, you always have the right to a private copy, et cetera. Often, people don't know better. And jurisdiction is different in every counry.
Therefore, unless the post looks egregiously illegal, assume it is being asked in good faith about removing DRM on things you own, for your own fair use.